1. Field of the Invention
The present invention generally relates to a planetary gearing for switching a plurality of power transmitting paths. It relates more particularly to an improvement of a mechanism for positioning a planetary gear at a predetermined position in accordance with the selected power transmitting path.
2. Description of the Related Art
As well known, the planetary gearing is utilized, in different manners, for a various mechanism. Typically, the planetary gearing comprises a sun gear, a planetary carrier supported by the same shaft supporting the sun gear, a planetary gear supported by the carrier so as to engage the sun gear so that it rotates itself and travels along the periphery of the sun gear, and a plurality of power transmitting gears which are arranged adjacent to the sun gear so as to be selectively engaged with the planetary gear. Further, the planetary gear can be held at the predetermined positions to engage one of the power transmitting gears in order to transmit the rotation of the sun gear to the selected power transmitting gear.
Supposing now, in the above-mentioned arrangement, that two power transmitting gears are arranged around the sun gear, stopper means, for holding the planetary carrier carrying the planetary gear at the predetermined first and second stop positions to engage the first and and second power transmitting gears may be arranged. The stopper means are respectively constituted by simple stopper members for preventing the overrunning of the carrier by contacting the outer sides thereof at the first and second stop positions. However, in the case where the number of the power transmitting gears may increase more than two, one and more stopper means must be additionally arranged in order to hold the planetary gear at the additional intermediate stop position(s). In order to hold the carrier at the respective stop positions for the power transmitting gears, the following methods may be provided: One is a lock means including a plural lock members, which are respectively arranged to hold the carrier at the desired stop or lock positions and movable between the lock positions and the retracted positions. It may be possible to control the carrier by detecting constantly the position of the carrier. However, these methods may disadvantageously bring very complicate mechanism or system.
The planetary gearing having the above-described arrangement is utilized, for example for a camera in which it is recently required that a plural operations such as film winding and rewinding, focusing and zooming are effected by less number of motors, more specifically such a mechanism for transmitting the power to more than two transmission gears is required. It is, however, noted that regarding the camera and the like, in which the numerous members must be assembled in a narrow space in the camera body, it must be avoided to make the internal construction of the camera and the control system thereof complicated.